In general, servo control systems utilize the concept of fixed-rate sampling, or temporal clocking, to obtain feedback sensor readings and maintain smooth control. A traditional approach to data acquisition in any high precision instrument such as a scanning tunnelling microscope (STM) also uses temporal clocking. In a STM, a high frequency clock is used to latch data as the data sensor moves over the surface of interest. The spacing of the data across the surface is a function of the clock frequency and the speed of the data sensor. The accuracy of the data spacing is a function of the ability of the servo control system to maintain a precise speed over the surface. This places extreme burdens on the servo control system as the desired precision of the instrument approaches atomic dimensions.
Using a single bit from a positional sensor (an interferometer in this case) to act as the data clock for a microtopographer instrument is disclosed in Teague et al., "Para-flex stage for microtopographic mapping," Rev. Sci. Instrum. 59, 67 (January 1988).